Problem: $ \left(\dfrac{3}{5}\right)^{-4}$
Explanation: $= \left(\dfrac{5}{3}\right)^{4}$ $= \left(\dfrac{5}{3}\right)\cdot\left(\dfrac{5}{3}\right)\cdot \left(\dfrac{5}{3}\right)\cdot \left(\dfrac{5}{3}\right)$ $= \dfrac{25}{9}\cdot\left(\dfrac{5}{3}\right)\cdot \left(\dfrac{5}{3}\right)$ $= \dfrac{125}{27}\cdot\left(\dfrac{5}{3}\right)$ $= \dfrac{625}{81}$